1. Field of the Invention
The present invention relates to a method and system for controlling a hybrid vehicle, and more particularly, to a method and system for reducing exhaust gas from a hybrid vehicle in a controlled manner.
2. Description of the Related Art
An air control valve (ACV) is a device commonly used for diesel engines in fuel-injected vehicles to combust injected fuels at or around a theoretically ideal air fuel ratio by measuring and adjusting air flow into combustion chambers. Functioning as a throttle flap of a diesel engine, an ACV blocks air inflow the engine is turned off to prevent dieseling and thus to reduce engine vibration. Additionally, an ACV forces the reduction of air intake upon exhaust gas recirculation to introduce exhaust gas recirculation (EGR) gas into an intake manifold. Further, an ACV has the function of adjusting air intake to adjust combustion temperatures to prevent catalyst devices such as a diesel particulate filter (DPF) from being damaged.
However, a conventional ACV is problematic in that when various incompletely combusted materials within exhaust gas are introduced into an intake manifold by EGR, some volatile organic compounds (VOCs) in the combusted material are attached onto the ACV to continually narrow the influx zone. In this condition, electronic control unit (ECU) mapping in consideration of the expected exhaust gas amount as a default may increase the exhaust gas level beyond a threshold level.
Accordingly, whenever the engine is turned off, multiple cycles of ACV opening and closing are performed to trap the attached, incompletely combusted materials or to adjust the closing degree of the valve. Unlike general diesel vehicles, diesel-hybrid vehicle engines frequently stop and restart based on road conditions and driving mode. The opening and closing of the ACV whenever the vehicle frequently stop may result in the generation of excessive noise and the reduction of the ACV in durability.
The matters described as the background arts are merely intended to increase the understanding of the background of the present invention, but should not be recognized as being prior arts which are already known to those skilled in the art.